Historically, the inner surface of a pneumatic tire is typically comprised of a layer of a rubber composition designed to prevent or retard the permeation of air into the carcass from the tire's inner air chamber. It is often referred to as an innerliner. Innerliners, or innerliner layers, have been used for many years in tubeless pneumatic vehicle tires to retard or prevent the escape of air, namely atmospheric air, used to inflate the tire, thereby maintaining tire pressure. Rubbers, such as butyl rubber and halogenated butyl rubber, often referred to as halobutyl rubber, as well as blends thereof, are often used for such tire innerliners which are relatively impermeable to air.
Historically, the tire innerliner itself is normally prepared by conventional calendering or milling techniques to form a strip of uncured rubber composition of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and their methods of preparation are well known to those having skill in such art.
Blends of natural rubber and emulsion polymerization styrene/butadiene rubber have sometimes been used to form tire innerliner layers in place of butyl rubber based innerliner layers to reduce the innerliner layer cost. However, typically, the resultant innerliner is less resistant to air permeation unless it is used as a thick layer.
In such rubber blends, it is envisioned that voids are present between the elastomer chains of the rubbers within the innerliner layer.
For this invention, it is desired to evaluate blends of cis 1,4-polyisoprene rubber, preferably natural rubber, and styrene/butadiene rubber together with a compatible resin where is envisioned that the resin may fill, or partially fill, such voids to aid in enhancing resistance to air permeability for an tire innerliner layer without the use of butyl rubber.
In the description of this invention, the term “phr” means parts by weight of an ingredient per 100 parts by weight of elastomer in a rubber composition unless otherwise indicated. The terms “rubber” and “elastomer” are used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” are used interchangeably unless otherwise indicated. The terms “rubber composition” and “rubber compound” are used interchangeably unless otherwise indicated.